In binding machines it is often customary to hold groups of signatures together in a series of mechanical clamps. (A signature is a large sheet of paper printed with four or a multiple of four pages, which, when folded, becomes a section of a book or magazine.) The clamps holding the signatures are advanced along a predetermined path to engage cutting and roughing saw blades by which the clamped signatures are cut along the edge which is to become the binding edge.
When clamping is accomplished the signature group is held in place by means of a spring biased clamp locking mechanism. The upper portion of the spring may be attached to an operating lever which controls locking and unlocking of the clamp, and the lower portion of the spring may be attached to a shaft, by means of hook-shaped elements extending from the spring body.
These clamp springs undergo a high rate of flexing, often several hundred times per hour. Due to this high rate of flexing, the springs sometimes break. When a spring fails, recoil can cause the remaining portion of the spring attached to the lower shaft to rotate either inwardly or outwardly. When a spring fails near its lower end attachment, the remaining spring segment attached to the shaft will swing down and hang from the hook-shaped element. As the clamp moves over the trimming and roughing saws, the saw blades and their plastic guard are damaged or destroyed. In the event a spring fractures near the top end attachment, if it rotates outwardly it will hang down and damage the saw blades; if it rotates inwardly it may contact the clamp carrier cam. Contact of the cam surface by the sharp end of a broken spring could render the cam useless. (The clamp carrier cam maintains alignment of the clamps throughout the clamping and trimming process. Each clamp is held to the cam surface by cam rollers. The cam surface must be perfectly smooth or damage to the cam rollers could occur.)
In addition to the damage to expensive machinery and the loss of productivity due to down time, operating personnel are in danger of being gravely injured by flying fragments of the saw blade and the plastic guard in the critical moments between the time the damage occurs to the machine and the stopping of the machine.